1. Field of the Invention
The present invention relates to microwave electronics. More specifically, the present invention relates to systems and methods for mounting circulators.
2. Description of the Related Art
A circulator is an electronic component with three or more ports that forces signals to travel between the ports in a particular direction. For example, in a three-port circulator, a signal fed to the first port is coupled to the second port only, a signal fed to the second port is coupled to the third port, and a signal fed to the third port is coupled to the first port. Circulators are commonly used in the front end of a RADAR system to couple a signal from a transmitter to an antenna, and a signal from the antenna to a receiver. A circulator can also be used as an isolator by adding a matched load to one of the ports.
Mounting and packaging front end circulators has always been a challenging task. The standard method of mounting circulators onto a printed circuit board includes attaching the ground plane of the circulator onto the board using a conductive epoxy and then wire bonding the signal ports to the board, typically using specialized selective gold plating. This process is inconsistent with typical low cost solder re-flow attach of integrated circuits to printed circuit boards and adds significant cost. An alternative approach is using rigid metal tabs to solder the signal ports to the circuit board. This approach involves a complex packaging for the circulator and a cavity cut out of the circuit board for proper mounting.
Several newer packaging technologies, such as pin grid array (PGA) and ball grid array (BGA), are available for mounting integrated circuits or chips that are simpler, cheaper, and more robust than wire bonding. However, these surface mounting techniques typically are not suitable for mounting circulators.
For example, a ball grid array (BGA) is a type of surface-mount packaging commonly used for mounting integrated circuits. A BGA mounted chip includes a plurality of electrical contacts arranged in a grid pattern on one surface of the chip and an array of solder balls attached to the electrical contacts. The chip is placed onto a circuit board having copper pads in a pattern that matches the array of solder balls, and then heated until the solder balls melt, thereby attaching the chip to the board. A BGA chip can therefore be mounted using a simple, single solder flow process, even if the chip includes hundreds of contacts.
Circulators, however, typically cannot be mounted using a BGA because of the geometry of a circulator. A circulator typically includes microstrip transmission lines for coupling the various ports. The microstrip signal lines are etched on a ferrite substrate over a ground plane, and a magnet is placed on top of the substrate over the microstrip lines. A magnetic return or pole piece is placed on the bottom of the substrate to direct the magnetic field of the magnet through the substrate, forcing signals to travel in the desired direction between the microstrip lines.
A conventional circulator therefore cannot be BGA mounted because the signal lines and ground are on opposite sides of the substrate. Integrated circuits typically use coplanar waveguides so that the signal lines and ground are all in the same plane. Conventional circulators, however, cannot use coplanar waveguides because the signals need to travel through the magnetized ferrite between the signal and ground planes in order for the circulator to function properly. Also, the additional components (the magnet and pole piece) above and below the signal lines and ground, respectively, can make it more difficult to package and mount a circulator.
Hence, a need exists in the art for an improved system or method for mounting circulators that is less complex, less expensive, and more robust than prior approaches.